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  • 1
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    Particle size distributions in Saturn's rings from Voyager 1 radio occultation (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Information on Saturn ring particle sizes obtained with the Voyager 1 ring occultation experiment is discussed. The theory underlying the determination of the particle size distribution is presented, including differential extinction and inversion of the scattered signal. Experimental observations and results for the observed spectra, differential cross sections, suprameter and sub- to suprameter size distributions are presented. The size and mass distributions both cut off sharply at about 4-5 m; the mass distribution peaks over the 3-4 m size range for four ring system features at 1.35, 1.51, 2.01, and 2.12 Saturn radii. A power-law type model is consistent with the data over a limited size range of 0.01 to 1 m. The fractional contribution of the suprameter particles to the microwave opacity for the four features appears to be about 1/3, 1/3, 2/3, and 1, respectively, and their cumulative surface mass per unit area are about 11, 16, 41, and 132 g/sq cm if the particles are solid water ice.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: (ISSN 0019-1035)
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The microwave opacity of Saturn's rings at wavelengths of 3.6 and 13 cm from Voyager 1 radio occultation (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Information obtained about Saturn's rings through radio occultation observations with Voyager 1 is discussed. The experimental aspects are addressed, including the positional relationships and relative motions of the spacecraft, rings, and earth, the radio system, observables, microwave opacity, and diffraction. The data characteristics, reduction procedures, calibrations, and corrections are described, and results are presented for the opacity, complex extinction, and diffraction. Ring C is found to exhibit a gently undulating structure of normal opacity, except for several narrow imbedded ringlets. The normalized differential opacity indicates a substantial fraction of centimeter-size particles. In the Cassini division, the opacity appears to be nearly independent of wavelength. Ring A appears to be nearly homogeneous over much of its width, but with considerable thickening near its inner boundary with the Cassini division.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: (ISSN 0019-1035)
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Synthetic aperture radar target simulator (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A simulator for simulating the radar return, or echo, from a target seen by a SAR antenna mounted on a platform moving with respect to the target is described. It includes a first-in first-out memory which has digital information clocked in at a rate related to the frequency of a transmitted radar signal and digital information clocked out with a fixed delay defining range between the SAR and the simulated target, and at a rate related to the frequency of the return signal. An RF input signal having a frequency similar to that utilized by a synthetic aperture array radar is mixed with a local oscillator signal to provide a first baseband signal having a frequency considerably lower than that of the RF input signal.
    Keywords: COMMUNICATIONS AND RADAR
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Saturn's rings - Voyager 1 radio occultation experiment results (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The Voyager 1 encounter with Saturn in 1980 included the first radio occultation measurements of the ring system. Opacity of and scattering by Saturn's rings were measured at 3.6- and 13-cm wavelengths using transmissions from the spacecraft to the earth. Detailed models of ring structure have been derived from these data at radial resolutions as small as 1 km, depending on the radio opacity of the region probed. Inverse power-law-type distributions of ring particle sizes with indices of about 3 and upper size cutoffs near 5 m are in good agreement with the data, but parameters vary throughout the rings. Occultation measurements have also provided information on ring dynamics and have led to a more precise definition of Saturn's pole vector.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); GE-22; 656-665
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Thickness of Saturn's rings inferred from Voyager 1 observations of microwave scatter (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Earth-based telescopic observations indicate that Saturn's rings are about 1 kilometer thick, while spacecraft measurements and theoretical considerations give an upper bound of about 100 meters. Analysis of a shielding effect present in radio occultation provides a sensitive new measure of the ring thickness. On the basis of this effect, Voyager 1 microwave measurements of near-forward scatter imply a thickness ranging from less than 10 meters in ring C to about 20 and 50 meters in the Cassini division and ring A, respectively. Monolayer models do not fit the observations in the latter two regions. The discrepancy between the earth-based and spacecraft measurements may be due to warps in the ring plane or effects of tenuous material outside the primary ring system.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 223; 396-398
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    On obtaining the forward phase functions of Saturn ring features from radio occultation observations (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: It is noted that the near-forward scattering functions of particles in Saturn ring features are related to 3.6 cm radio occultation power spectra by a Fredholm integral equation of the first kind. The equation reduces to an algebraic system of equation whose solution by usual inversion techniques (that is, least mean squares) is ruled out by the near singularity of the forward transformation matrix. A combination of constrained linear inversion and a filtering algorithm based on eigenvector decomposition of the matrix reduces the instabilities; this yields derived phase functions valid over the range of zero to about 12 mrad. It is noted that these functions represent the collective forward diffraction lobe of particles greater than about 1 m in radius. Since multiple scattering of the signal is a significant effect, the measured phase functions must be adjusted to obtain the singly scattered component. This single-scattering correction is examined for two physical models, namely the monolayer and the classical discrete random slab; in addition, the fraction of opacity in submeter particles for each model for particular ring features is estimated.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 56; 209-228
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Simulation and studies of spaceborne synthetic aperture radar image quality with reduced bit rate (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A computer simulation program that is used to study the effects of digitization in spaceborne synthetic aperture radar systems is described. An analytical study of the distortion noise introduced by the digitization process at various gain settings, sampling rates and bit error rates is presented and the results agree well with those obtained from the simulation program. The simulation program is also used to study the spatial frequency response of hard-limiting (quantizing to 1-bit) synthetic aperture radar systems. The implications of these results on synthetic aperture radar system design are discussed.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: International Symposium on Remote Sensing of Environment; May 11, 1981 - May 15, 1981; Ann Arbor, MI
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    A digital Seasat SAR correlation-simulation program (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A correlation-simulation program for processing Seasat SAR data is presented, featuring the use of FORTRAN code to allow simple transference to another computer. The highest attainable azimuthal resolution for Seasat SAR experiments and the ability to generate images with varying quality by varying resolution or the number of looks are additional features. A fiber optics link transfers the Seasat data from high intensity digital tapes to an SEL 32/55 computer, and the least significant bits of the 5 bit data samples are truncated, thus the input data have 4 bits per sample. A total 8192 echoes are processed each time and stored on 8 separate data files on the disk. In addition, a program operating on 1-look high resolution images for performance simulations of proposed radar systems and processing schemes has been completed. Finally, the coding is simple, and 8 hours are required to process one image using this program.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: International Geoscience and Remote Sensing Symposium; Jun 08, 1981 - Jun 10, 1981; Washington, DC
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    NASA TECHNICAL REPORTS
  • 9
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    Thickness of Saturn's Rings Inferred from Voyager 1 Observations of Microwave Scatter (1984)
    American Association for the Advancement of Science
    Details
    Publication Date: 1984-01-27
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science
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